Quote from: JanusAgain, since the m here refers to proper mass, it doesn't apply to a photon. Instead, the momentum for a photon is found by
p = hf/c
And the general equation ends up giving you E= hf for the photon.
I understand both equations (surprise!), but am not clear as to how p = hf/c becomes E= hf.
Energy is momentum times velocity. Here it is pc. Since hf/c times c cancels out the speed of light you are left with E = hf.
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